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2010-2011 Graduate Fellows

Dartmouth GK-12 Project

Seth Cohen, Physics and AstronomyGary Wegner, Thesis Advisor

All matter in the universe interacts through the force of gravity. Stars group together into galaxies, and galaxies clump together to form groups and clusters. These galaxy clusters are the largest structures in the universe, and even they can be pulled towards each other. When clusters are gravitationally attracted to each other, they can merge and interact in fascinating ways. This merging of galaxy clusters is the focus of my research.

I observe with both ground- and space-based telescopes, using visible light and X-rays, to illuminate different parts of galaxy clusters. Clusters are made of three main components: galaxies, gas, and a mysterious type of undetectable matter known as dark matter. When clusters merge, these three components interact in different ways, lending insight into how all structures in the universe form and evolve. For example, when gas from one cluster collides with gas from another cluster, it heats up and condenses, forming stars. I measure how this star formation changes based on how crowded parts of a cluster are or how galaxies are moving within a cluster. Studying how stars form in clusters can help astronomers understand how mergers help shape the universe, how galaxies like our own formed and evolved, and where the universe is headed in the future.

Ronald Kinser, Biological SciencesPatrick Dolph, Thesis Advisor

A glistening sunset…a beautiful painting…a loved one’s smiling face. Every year retinal degenerative diseases rob hundreds of thousands of people of life’s simple joys. My project explores the mechanisms leading to the destruction of photoreceptor neurons. Photoreceptor neurons are essential for vision, thus their death leads to blindness.

To study photoreceptor cell death we use the common fruit fly, Drosophila melanogaster. Drosophila visual physiology is remarkably similar to that of humans, and therefore provides a powerful means of modeling human retinal disease. To study retinal degeneration, we have taken advantage of a group of fruit flies that become blind. The most interesting aspect of these blind flies is that their photoreceptors have difficulty shuttling proteins when they are exposed to light, thereby causing photoreceptor cell death. Endosomes are one of the main groups of protein shuttles inside the cell. My hypothesis is that these endosome shuttles are breaking down in blind flies, causing their internal contents to spill out inside the cell, wherein they can cause cellular damage.

Cathepsins are intra-endosomal proteases (proteases chew up proteins) previously shown to be involved in cell death and, therefore, represent good candidates to cause cellular destruction. If cathepsins are involved in mediating cell death in light exposed blind flies, then blocking the activity of all cathepsins should prevent retinal degeneration. When cathepsin inhibitors are present in abundance, retinal degeneration does not occur.

This data represents a step forward in identifying the causes of photoreceptor cell death and may represent a general mechanism for a broader group of neurodegenerative diseases.

Robert McGarr, Physiology and NeurobiologyVal Galton, Thesis Advisor

Heart attack is a leading cause of death in the United States and one important indicator of patient survival from heart attack is the level of thyroid hormones in their blood. The greater the decline in thyroid hormones in the blood after heart attack the more likely it is that the patient will die. These observations in humans have been recapitulated in models of heart attack in several mammalian species and it is well known that thyroid hormones are important mediators of heart function in mammals. I model heart attack in mice in order to investigate the role of thyroid hormones in recovery from heart attack because I am able to manipulate thyroid hormones in the heart directly.

In addition to the level of thyroid hormone in the blood, there is a specific protein that controls the amount of thyroid hormone present in the heart; this is the type 3 deiodinase (referred to as D3). D3 is an enzyme, or a biological catalyst, the primary function of which is to inactivate thyroid hormones in order to protect the heart from excess amounts of them. We have observed that D3 activity increases after heart attack and that the activity is specifically localized to the injured region of the heart during recovery. This observation suggests that limiting thyroid hormone concentration in the injured region of the heart is important for recovery from a heart attack and that there are localized molecular mechanisms responsible for this. Manipulation of thyroid hormones in the injured heart through specific mechanisms of mice may result improved recovery from heart attack and ultimately allow us to translate our findings from mice into clinical therapies that would benefit patients recovering from heart attack.

Julie Skinner, Physics and AstronomyJohn Thorstensen, Thesis Advisor

Roughly half of the stars in our galaxy are linked to another star in a binary system – that is, two stars orbit each other in a way similar to the earth revolving around the sun. As an astronomer, I study a specific class of binary systems where two stars are close enough together that one gives up material to the other star. These types of systems are known as cataclysmic variable stars or CVs. CVs help us understand how stars change over time and how stars can interact with each other. To carry out my research, I first look for the length of time it takes the stars to revolve around each other. This is known as the orbital period. Analogous to the earthʼs 365 day orbit around the sun, CVs typically orbit in less than one earth day. Sometimes it takes only minutes! Knowing the orbital period allows me to calculate other facts about the system, such as the amount of matter contained in the stars and how the system changes over time. To gather information about CVs, I use the telescopes at the MDM Observatory near Tucson, Arizona. The instruments on the telescope allow me to break up light from stars into their spectrum in the same way that a raindrop or a prism breaks up sunlight to make a rainbow. The different wavelengths of light give me the information I need to calculate the orbital period. Learning about CVs enables astronomers to determine what kinds of stars are in our galaxy and how theyʼre grouped, which allows us to better understand how binary star systems influence the structure of our galaxy.

Which is smaller: 1/2 or 3/8? Although fractions should be mastered by fourth grade, just half of eighth graders in America can correctly answer 3/8. As a cognitive neuroscientist, I use MRI, a powerful camera, to peer inside the brain to explain why certain kinds of math like fractions are difficult to learn. Neuroscientists (or brain researchers) have shown that the brain often mistakes numbers that are close together for one another. For example, if a single brain cell mostly sends messages about the number eleven, it will also communicate information about ten and twelve, but less regularly. Ultimately, eleven becomes unclear, and a quick glance at eleven roses can easily be mistaken for a dozen. People also make the same mistake when comparing numbers in digit notation (like 11 and 12) if they have less than half a second. As we learn digit notation our brains dramatically change and our ability to think about numbers becomes more exact. We stop using the inferior frontal gyrus, a part of the brain used for critical thinking, and use the intraparietal sulcus, a part of the brain used by adults to think about numbers. Although number processing in the brain seems well understood, all of these findings are based on research with whole numbers. When adults think about fractions their brain responds like a child-- imprecisely and requiring critical thinking. My research will determine why the brain processes fractions differently in order to help children understand that 3/8 is less than 1/2.

Morgan Thompson, Biochemistry Jon Kull, Thesis Advisor

Certain cells are constantly moving from one locationto another within the human body. A number of cells involved in the immune system circulate in the blood until they receive a message of distress from damaged or infected tissue. Upon receiving this signal, immune cells will completely change their shape by transforming from a sphere to a flattened disk so they maycross the barrier of the blood vessel wall to enter the site of infection. The shape of a cell is maintained by a skeleton comprised of protein molecules just as the shape of a human body is maintained by bones of the skeleton. One of the cell’s skeletal proteins is called actin. Many actin molecules combine end-to-end to form a filament, a rigid structure that resembles two stands of pearls wound around each other. These filaments push up against the inner edge of the cell and can grow and shrink in length to allow for changes to the overall shape. Multiple proteins interact with actin to control filament growth including formins. Two formin molecules will come together in a ring at the tip of an actin filament to slow down its growth. However, these proteins are so small that they cannot be seen by even the most powerful light microscope. I use X-ray crystallography to visualize formins bound to actin on a submicroscopic level. This technique employs X-rays to take a series of images of the protein complex in a crystalline form. These images are then combined and reconstructed to give a three-dimensional molecular view of a formin ring around actin. Ultimately, this work will provide us with information about how actin molecules associate with each other and how they interact with formins; bringing us closer to understanding the complexities of cell movement throughout the body.

Karl Yando, Physics and AstronomyRobyn Millan, Thesis Advisor

My research concerns geospace. I study outer space, where stars lose their twinkle and the sky is black, but not the stars themselves or even our neighboring planets. Rather, I study our planet and the space surrounding it. In particular, my work concerns the Van Allen radiation belts—vast populations of protons and electrons that are freed in the vacuum of space to zip around Earth like an enormous number of speeding bullets.

It can be a harsh and unforgiving environment, and these particles do real damage to spacecraft electronics and astronaut DNA. In a different context, these particles are the cause of one of nature’s most spectacular displays—the aurora borealis of the northern sky. These particles have a story to share, and we seek to understand it.

In this endeavor, we employ the complementary capabilities of satellites and high-altitude balloons. The former provide us with direct measurements from the near-Earth space environment; the latter provide us a low-cost platform at the edge of space. Our current project will loft some 40 balloons in conjunction with an upcoming NASA satellite mission. Looking upwards from each balloon with an x-ray “camera,” we can see energetic electrons come crashing into the atmosphere. A satellite passing overhead will see these same particles, but from a very different vantage point. By making simultaneous measurements from many locations, we hope to better map the evolution of the radiation belts. In doing so, we help keep our assets safe through better forecasting of the geospace radiation environment.